Alcoholic liver disease is caused by chronic heavy drinking, and is one of the major causes of liver cirrhosis. Thus, it is important to assess drinking behavior in all patients who present with liver disease. However, obtaining an accurate drinking history can be difficult, as the specificity of alcohol biomarkers is low in this population, and obtaining an accurate history by self-report or through collaterals is prone to error. Blood phosphatidylethanol (PEth) is an ethanol metabolite and novel biomarker that has undergone several small validation studies in substance abuse settings. While this early validation work appears promising, the characteristics of PEth for detecting clinically important levels of drinking in a more representative clinical population are largely unknown. Our pilot work began to address this issue in patients with liver disease, and suggests that PEth is highly sensitive for at least moderate to heavy drinking in this group. The studies described in this application further characterize the relationship of PEth to the amount of alcohol consumed in patients with liver disease, determine the accuracy of PEth for differentiating clinically important levels of recent drinking, and determine if PEth is superior to a well-studied alcohol marker (%CDT) in this population. Pertinent to the ultimate clinical utility of PEth, a secondary goal is to assess the association of baseline PEth with subsequent clinical outcomes. If highly valid, the clinical use of PEth will improve many facets of care for liver disease. This includes diagnosis of alcohol-related liver disease, assessment of response to treatment for heavy drinking and alcohol use disorders, early identification of relapse, and selection of the most appropriate candidates for liver transplantation. Findings may also have implications for other clinical populations (e.g., obstetrics, primary care, trauma), for evaluating the epidemiology of alcohol-related problems, and as a surrogate end-point in treatment outcomes research. PUBLIC HEALTH RELEVANCE: RELEVANCE Chronic heavy drinking is a common cause of serious liver disease, and abstinence or substantial reduction in drinking is the only effective treatment;however, physicians do not have clinically useful, objective measures of heavy drinking in patients with liver disease. This research will evaluate blood phosphatidylethanol, a novel marker of heavy drinking, in liver disease patients. Results may provide health care providers with an important tool for detecting heavy drinking, for monitoring response to alcohol treatment, and for early detection of relapse.